The osmotic fragility test of erythrocytes has been a relatively insignificant clinical test in medicine. The conventional Parpart method (see A. K. Parpart, P. B. Lorenz, E. R. Parpart, J. R. Greeg and A. M. Chase, "The Osmotic Resistance (Fragility) of Human Red Cells", J. Clin. Invest. 26:676, 1947 ) using multiple test tubes, is too cumbersome and time-consuming with respect to the value of the information derived from a few critical hemolysis points on an integrated curve.
In recent years, two improved methods have been reported which produce an entire hemolysis curve. The curve can be obtained with the method of Dannon (see D. Dannon: "A Rapid Micro Method for Recording Red Cell Osmotic Fragility by Continuous Decrease of Salt Concentration", J. Clin. Path 15:377, 1965 ) by subjecting cells to a gradual change of osmolarity by means of dialysis, while monitoring the change of transmittance of light through the solution. It uses a dialysis chamber equipped with a pair of celophane membranes to hold the sample solution. Dialysis through the membranes produces a gradual decrease of osmolarity in the sample solution. This osmotic gradient is a function of the distance between the two membranes and the integrity of the membranes itself. Therefore, slight dislocations and alterations of the membranes may affect the reproducibility of the results.
In the coil planet centrifuge technique (see R. Harada, Y. Ito, and E. Kimura: "A New Method of Osmotic Fragility Test of Erythrocytes with Coil Planet Centrifuge", Japanese J. of Phys. 19:306-314, 1969, and K. Katzimer and S. Shibata: "Coil Planet Centrifuge and its Application to the Observation of Altered Membrane Properties of Erythrocytes in Hepatobiliary Disorders", J. Lab. Clin. Med. 85: 855-864, 1975 ) a fine coiled tube is filled with a solution containing an accurate osmotic gradient. Blood cells introduced at the high osmolarity end of the coil move through the gradient solution at a predetermined rate determined by the slow rotation of the coil under the centrifugal force field. When the cells reach a critical portion of the gradient, they release the hemoglobin, which remains at this position within the coil, which then can be scanned along its length by means of a densitometer. One advantage of this method is that hemolysis takes place within a pure salt solution free from hemoglobin, since released hemoglobin is always left behind, and the intact cells are constantly washed with a new solution as they travel through the coil. Although this technique has advantages, it is rather cumbersome to use and is limited by the difficulties in accurate analysis of the hemolysis curve due to the poor optical properties of the tube wall.
For these reasons, most of the clinical laboratories are still using the conventional Parpart method for the osmotic fragility test of erythrocytes.